Treatment of vegetable tissue



manner.

Patented June 2a, 1949 .UNITED STATES PATENT OFFICE Clarence Birdseye, Gloucester, Mass; designer to Dehydration, Inc., Gloucester, Mam, a corporation oi Massachusetts No Drawing. Application June 21, im,

Serial No. 541,459

is possible when such vegetable matter. is blanched 5 in either water or steam in accordance with current commercial practices. More specific objects of the invention are to permit the blanching of vfruits without causing them to take on a "cooked" appearance and flavor; to blanch vegetables with substantially no loss of any of their water-soluble elements; to facilitate penetration into vegetable units of edible materials which have been applied tothe exterior thereof before blanching to regulate and control loss of weight during blanching;

to provide facilities for both blanching and dehydrating continuously in the same apparatus; and ingeneral to produce irozen and dehydrated vegetables and fruits of high quality in an eiiicient According to present commercial practice, practically all vegetables and some fruits which 2 arev to be frozen or dehydratedare first given a treatment with hot water or steam to inactivate their enzyme (particularly catalase and perioxidase) content. This treatment has for many years been known as blanching and usually consists in raising the temperature of all parts of the moist material to at least 185 F. and maintaining that temperature in the product for at least iive seconds. Many types of commercial blanching apparatus are available, and all of them use either water at or near the boiling point or steam at atmospheric or greater pressures. Bianching is-so well understood and so universally applied in the processing of vegetables for trees-h ingand dehydrating that details or the procedure need not be described herein. However, there is given below a table of standard blanching times with both hot water and steam as a blanching Vegetable val-mm nut Suited $332 gg g gf gg new. ma mu m ch momma 23 Beets Crosby Boiling water 13; Over Beet greens do do 2. I i Carrots, sliced (3 in.)-- Nantes Curly mustard Giant Southern Gui-led Mmterd. Ksle-.-. Tall Ourled Scotch Kale Kohlrsbi, diced Early White Vienna mum I New Zealend spinach- Sm Swiss chard Lueniius--.-.

%T;;ia;::::::: e01

' Small stalks 3 Asparagus. Washingt n Steam Large stalks:

' v Small beans, 1. Beans, lime Henderson Boiling water Mediuliransbeansz 1%.

" i e entucky Wonder Beans, snap glue Lake- ....do 2.

I Small pieces, a Broccoli Italian Green Sprouting do Medi uxn i g eces, 4% Cauliflower Snowball do ggg gg ge g 4 homes Lexton Small Pm {idol-man 1%, 1 8.21 1 51111111121: "I

6 How Golden Bantam. m on Golden Cress Bantam. F i-row Golden Bantam out Golden Bantam Present commercial methods of blanching are highly objectionable because they subject the product to the leaching action of hot water. This is true whether the product is blanched directly in. hot water orby subjecting it to the action of steam at or above atmospheric pressure-for when steam' is used, considerable amounts of the steam are condensed onto the relatively cool surfacesof the product units during the blanching process. A further disadvantage of steam blanching is that if the product units are to be evenly blanched, they must be either spread in a very thin, uniform layer or must be thoroughly stirred throughout the blanching process. Stirring during' blanching is sometimes highly undesirable; for it inevitably abrades, or even breaks, the units of such delicatevegetables as white and sweet potatoes.

Another objectionable feature of present methods is that facilities for such blanching cannot readily be incorporated as an integral part of a dehydrating apparatus. Still another undesirable characteristic of present blanching practice is that when vegetables and fruits are blanched in hot water or steam, it is necessary to overheat the surface areas of the product units (or of the mass of units, if blanching is done by heating an aggregation of units) in order to heat the m terior of the units to thetemperature required for enzyme inactivation. For example, corn-on-cob intended for freezing must be heated in live steam for approximately seven to nine minutes (depending on the ear size) in order to bring the center of the cob to the necessary blanching temperature. Cubed white potatoes intended for dehydration must be blanched in hot water or steam till their centers are heated to approximately 190, F by which time the corners and edges of the cubes are so overheated that they suffer considerable abrasion even when handled gently during: sub-. sequent processing. Slicedripe fruits, for either freezing or dehydrating, become mushy on the surface if blanched in either hot water or steam.

I have discovered that all of the shortcomings of present blanching methods can be overcome by the use of heat generated directly within the vegetable units by high-frequency electric fields. In such fields the temperature of the product is rapidly raised to the desired point throughout its mass. Heat generated in the product in this manner permits effective and accurate-blanching without bringing any extraneous waterinto contact with the surfaces of the product units, and thus avoids completely the leaching action of hot water and steam. Moreover, no stirring of the product during blanching is required; for heating is uniform throughout the mass regardless of the thickness of the mass.

Another advantage of my presentv invention is that moisture .loss from the product during blanching can be accurately controlled merely by regulating the humidity of the gas surrounding the product during the blanching process. For

if the product layer is relatively thin and'if the surrounding atmosphere is arid, considerable moisture will be evaporated from the product during the blanching process. If, on the contrary, the product layer is quite (several inches) thick and if the atmosphere surrounding the product has a relative humidity of approximately 100 per cent, no moisture can be lost during blanching. Moreover, since the product will at all times during blanching be hotter than the surrounding atmosphere, no moisture oanbe condensed onto the product from that atmosphere.

By the process of my co-pending application Serial No. 536,422, vegetables intended for dehydration are first drenched with very hot water, next treated with a cooler solution containing edible materials to be added to the vegetables, and then blanched. The edible material penetrates into the vegetable units as their tissues are killed by the heat of blanching.- If, however,

a steam blanch is used, water condensed from the steam upon the vegetables dilutes and partly washes away the film of edible solution previously applied. This necessarily results in imperfect penetration into the product by the edible materials contained in the solution. My present meth- 0d of blanching by high-frequency heat generated in the product itself completely eliminates the foregoing diihculties.

Certain fruits (e. g. strawberries) are seriously damaged by excessive heat and can be safely blanched only by prolonged heating at low temperatures; e. g. two to four minutes at 175R 1'. I prefer to subject such fruits lntermlttently'to the action of high-frequency fields. By this means the entire unit of product can, without danger of overheating, be alternately brought to any desired temperature, allowed to cool slightly, and then again heated to the maximum temperature desired. Moreover, by my method of alternately heating and cooling as described above, even heat-sensitive products may be safely not only blanched, but actually pre-cooked to any desired degree.

Many fruits, for example berries and sliced peaches, are improved in color, flavor, consistency, and aroma if they are blanched while coated with sugar, a neutral sugar-salt film, an acid protecting film or glycerine and acetic acid, or some other edible substance which protects the surface of the fruit from oxidation both during and after blanching and also penetrates into the fruit by osmosis to firm the. fruit tissue. Neither steam nor hot water can be used satisfactorily for blanching such coated fruits, for the water removes or dilutes much of the coating. But blanching in a high-frequency electric field, in accordance with my present invention, does not bring extraneous water into contact with the coating on the fruit and does facilitate penetration of the coating into the product.

Incertain instances-e. g. ripe plums-it is desirable to blanch the product while submerged in a protective solution, such as sugar syrup, the

' product being blanched by heat transferred to it from the hot syrup. This type of blanching has been tried experimentally but has not come into commercial use, because the fruit is over-heated at its surface before it is sufficiently heated at its center. By the method of my present invention, however, the fruit and the protective substance in which it is submerged are simultaneously heated throughout by the action of the high-frequency electric field in which they are placed. Thus my invention for the first time makes blanching in a sugar syrup or other liquid commercially practica e.

As pointed out in my copending application Serial No. 536,422, it is often desirable to add an alkaline substance-e. g. sodium bicarbonate-to vegetable tissue for the purpose of tenderizing it. An objection to this method of rendering dehydrated vegetable tissue tender is that only very limited amounts of the alkaline substance can be used without adversely affecting both the flavor and the ascorbic acid content of the tissue. I have found, however, that very great enzyme. such as pepsin or papain, or another suitable active enzyme. I prefer to accomplish this by blanching the vegetable tissue in a highi'requency electric field to in actlvate'enzymes Exmrnrs or Paocass Sliced apples Pare and core sound, ripe apples of any va- 50 riet'y. cut into eighths, dip in a light sugar syrup (50% by weight), place in a three-inch layer on a belt conveyor of dielectric material, and

subject both the belt and the material to an alternating current field of approximately 15 product pieces may be either frozen before or after packing, or dehydrated in an apparatus according to the disclosure of my prior Patent No. 2,419,876.

- Dehydrated cabbage Core and shred cabbage in the usual manner. Place the shredded product in a 3-inch layer on an endless woven-wire, stainless-steel belt,

three seconds, drain for ten seconds, shower with a 130' 1''. aqueous solution containing M. of 1 per cent each of sodium bicarbonate and sodium sulphite and 25 per cent glycerine by weight, drain 5 for twenty seconds, transfer to a layer three inches thick on an endless belt of woven asbestos fibers impregnated with a synthetic resin, and pass through a high-frequency field of approximately 15 to 25 megacycles per second until found in the living tissue, removing approxithe temperature of the product mass has been mately 60 per cent of the moisture irom the raised substantially uniformly to approximately blanched tissue, causing the partially dehydrat- 200 P. Then, without allowing the blanched ed tissue o s r an q s ion of t product to cool substantially, run it onto the up- Dr y i en yme. and then further dehydr permost belt of a dehydrating apparatus similar ing the vegetable. to that disclosed in my prior Patent No. 2,419,878. The pr c ss of'm r s nt inv ntion an In the dehydrating apparatuadry the cabbage pp ie as a Preliminary ment for vegetable -to a residual moisture content of approximately tissue which is to be either frozen or dehydrat- 4 per cent. Then remove the dried cabbage from ed. When the product is to be dehydrated, I the dehydrator and package in moisture-vapor- Drefer t use an apparatus o the typ disclosed proof cellophane or other material equally imin my tic-p n g p c i $eria1N0-456,903, pervious to the passage of moisture vapor at filed Sept. 1,' 1942, now Patent No. 2,429,876, room temperature, dated Apr 1 In that case I use dielec- In dehydrating cabbage and other leafy vegtric material for the p l of the apparatus etables, it is desirable to compact the product and preferab y p s the product o that belt before blanching it in order to reduce the volpeatedly throu h high-frequency fields before it ume of the product and the thickness of the is su j to e h g r t n rgy, and layer which must be passed between the elecconducted heat which characterize the said t d greatlng the high-frequency field. This fll p e-t Depending up the y o ihstfllis important because power cost runs up as the lation desired. the blanching m y take Place on 30 distance between the electrodes increases. Acthe top belt either before or immediately after cordingly, in carrying out my process I may pm. t product enters the upp os t l in the ceed by advancing the leafy vegetable in a loose pa at In certain instances where the r layer upon a conveyor belt and then compact uct pieces are relatively resistantto breakage or thi layer by passing it between rollers on its abrasion even afte being blanched (e. g. carway to the high-frequency blanching field. rots). I may p ly stir the product mas In blanchin fruit or other products in a liquid while it is Pass g f om One high-frequency field syrup, I have found it advisable to provide for to the next time accele 'et d evaporation of actual electrical contact between the electrodes moisture from the p od and e. co s en and the liquid in which the fruit is immersed cooli f t e p o uct un ts. W en ve tabl 40 since by so doing I am able to achieve-a faster tissue is to be frozen. I have found that it is and more economical blanching operation. This S met m advantageous to place the tissue in constitutes a further novel step of my process a consumer Package and e ch the tissue and may be efiected by providing the uppermost in the package by he ing both tiesue nd p electrode with drag wires or strips which will ageinahigh-Irequency electric field. enter the liquid solution as the product being treated is passed between the electrodes.

I have referred hereinabove to the treatment of various vegetable units by immersing or spraying them with a solution containing various.

agents for protecting or improving the product. I contemplate, however, treating fruit or vegetable units by a dry process of dusting with powder: for example, I may mix powdered sugar, sodium sulphite, and sodium bicarbonate in the proper proportions and dust the cut vegetable units with this powdered mixture before subjecting them to the action of a high-frequency electric field. In this way I cause the powdered agents to penetrate into the vegetable tissue after it has been killed in the blanching step, and all this is effected without any leaching or diluting tendency, and, if desired, simultaneously with an initial stage of dehydration.

Having thus disclosed my invention and described in detail several examples of its practice t. in the treatment of illustrative products, I claim as new and desire to secure by Letters Patent:

51 In the treatment of vegetable material, the step for blanching to inactivate the enzyme contentkpf vegetable tissue without bringing extraneous water into contact with exposed tissue surface and without material loss of solubles from the tissue, which consists in heating the tissue in a. high frequency electric field and in an atshower with boiling water for approximately mosphere of predetermined humidity whereby moisture loss from the material may be controlled during the blanching process.

2. A process according to claim 1, in which the vegetable material is repeatedly heatedwith intermittent periods of cooling, in a high frequency electric field.

8. A process according to claim 1, in which the vegetable material is first pressed into compact form and then blanched in a. high frequency electric field.

4. A process according to claim 1, in which the vegetable material is maintained during the blanching step in an atmosphere of high relavtive humidity and evaporation of moisture from the vegetable tissue thus retarded.

5. A process new to claim 1, in which the vegetable is blanched in a high irequency elec= trio field. and then packed in a container and iroaen.

6. In a p w.- according to claim 1, in which the vegetable tissue is t enclosed in a nonmetallic coner wherein it is to be marketed, heated in a high frequency electric field while so contained and while tree from contact or extraneous moisture, cl thereafter subjected in said container to refrigeration to preserve it.

7. A pr to cia 1, in which the vegetable units are first :rched in a h ireuuency electric fieln and while free from contact of extraneous and then subjected to a. A p t h s" 2: t0 (3] 1, in which the blanched egetable material h partially dehy= drated, edible substances added and the vegetable material then ffer dehyteqi 9. A process aecog to claim 1, in which the vegetable mm are first pretreated with an edible substance and then blanched in a high frequency electric field while free from contact with extraneous water.

10. An improved process of treating vegetable file of this patent:

UNITED STATES PATENTS Number Name Date 1,035,777 Bullock Aug. 13, 1912 1,863,222 Hoermann June 14, 1932 1,900,573 McArthur Mar. 7, 1933 1,914,947 Golden June 20, 1933 1,945,867 Rawls Feb. 6, 1934 r 3,992,515 Uhlmann Feb. 26, 1935 2,091,268 Ball Aug. 31, 1937 2,112,418 Hart et a! Mar. 29, 1938 2,131,431 Fiske Sept. 27, 1938 2,228,783 Smith Jan. 14, 1941 FOREIGN PATENTS Number @ountry Date 5118.333 Great Britain 1939 OTHER REFERENCES Thermex High Frequency Heating, pub. by the REFERENCES CITED The following references are of record in the Girdler Com. Louisville, Ky. 1942, page 9.

Modern i'ackaging, Feb. 1944, .by V. W. Sherman. Institute of Food Technologists, 1944, published by the Gerrord Press, Champaign, 111., pages 89 and 90. 

